DUO registration for dual Dutch-American student

Hello all, I'm a uni student from the US, but I'm also a born Dutch citizen. I also go to a university in the US. I was trying to make an account with DUO to see if I could apply for financial aid, since everything is so expensive, but they told me I need a BSN, which I don't have, since I've never lived in the Netherlands. Anybody here been in in a similar situation or have any advice for how to go forward?